Process for the production of oxygen and nitrogen



G. CICALI Aug. 12, 1930.

PROCESS FOR THE PRODUCTIJN OF OXYGEN AND NITROGEN Filed June 20, 1925 iii r m mm mm .[W. 8 70/ Patented Aug. 12, 19 30 UNITED STATES PATENT orrlca GIOVANNI CICALI, OF BOLOGNA, ITALY PROCESS FOR THE PRODUCTION OF OXYGEN AND NITROGEN Application filed June 20, 1925, Serial No. 38,591, and in Italy February 16, 1925.

This invention relates to the process of producing oxygen and nitrogen by the distillation and rectification of air and has forits object to render the process more expeditious and considerably cheaper. y

The production of pure oxygen and nitrogen from the air by distillation and rectification has hitherto een accomplished by the compression of all the air to the maximum in pressure used in the cycle.

Instead of compressing to the maximum pressure all the air used in the cycle the entire volume of air is subjected to a low pressure, about three atmospheres, after which it is divided, in any suitable manner into two volumes being, approximately and 70% of the whole. I

The smaller volume of air is then cooled at constant pressure until its'temperature ap- "lfl proaches the saturation temperature for said low pressure, whereupon this smaller volume of air is introduced into therectifying column.

The larger volume of air is compressed to 2 the maximum pressure of the cycle, in any suitable manner,'and is then cooled at that pressure to a'temperature of about -100 C., which is higher than the temperature reached byjhe smaller volume of air under low pressure. This larger volume of air is then divided into two parts in the proportion of about 20% and of the whole. The smaller volume of highly compressed air is cooled and. thenthrottled before introduction into'the rectification column, while the larger volume of highly compressed air is first cooled, then'throttled and finally ,ex

panded to the low pressure before introduc tion into the column.

49 The rectification column is provided with a system of bafiles and trays so arranged that the various components of the air can be led off through interconnected cooling coils which efiect the'aforementioned cooling of n the air and which conductsaid components to any desired location.

The operation of this process will be un- H derstood by reference to the following description and the drawing:

The single figure is adlagrammatic illusand the remaining nitrogen tration of various steps in the accomplishment of this process.

,The whole of the air to be treated, previously purified, is conveyed into the low pressure cylinder C where. it is compressed to.a

few atmospheres, the heat developed being extracted by means of water refrigerating the walls of the cylinder C and the externalcoil -s so as to cool down the air after the first compression to a temperature being but slightly above that of the refrigerating fluid.

The low pressure air issuing from the cylinder C is divided into two portions; one portion, weighing P, is conveyed through the cockR to the two-pipe heat exchange coil S and flows inside of the coils inner pipe, while the outer pipe of the coil, as will be seen later on, is traversed in opposite direction by a certain amount ---:I: of nitrogen which has already been rectified and is extremely cold.

' In the 0011 S 'the air amount P is cooled nearly down to the saturation temperature corresponding to the air pressure. The air issuing with this temperature from the coil S is led by the pipe A into the rectification column. The other air portion weighing 1-'-P (assuming. that l lzilogram of air is bein considered as under treatment) is conveye through the cock R to the other compressing cylinders (viz. C where it is compressed up to'the maximum final pressure. Also the compression taking place "in C is effected under simultaneous extracting of heat, water being used as refrigerating me- On'i'ssuing'from C the air portion 1-1 is led through the water-cooler -s where. the pressure remaining nearly unaltered, it approximately takes up the temperature'o the water. This air then enters the middle pipe of a heat-exchange apparatus S con sisting in a three-pipe coil, through which flow in opposite directions the already rectified and cold oxygen inside of the inner pipe likewise already rectified and cold) inside of theouter pipe. In the heat-exchange apparatus S the temperature of the air portion (1-P) sinks far below that of the surrounding 'athas liquid down mosphere. The air issuing from S is divided into two subdivisions; one subdivision is led through the cock R to the expanding vessel e wherein its temperature in consequence of the expanded work, is further lowered, and is then delivered by the pipe A into the column. The other subdivision is liquefied and cooled, approximately at the maximum pressure reached in the compressing cylinders 0 by the heat-exchange apparatus S this air flowing inside of the inner pipe of and the outside surface of this pipe being licked by the nitrogen portion Y that will afterwards circulate through the outer pipe of the heat-exchange apparatus The air that has been liquefied and cooled in S is throttled by the cock R down to the pressure obtaining at inlet C of the column into which the'air is delivered.

The air entering the column at N on its upward travel, is obliged to traverse the pans DD, the aggregate of which forms a kind of bafile for the purpose of obliging the greater portion of the oxygen to condense in the bottom portion of the column. The liquefied oxygen drops through the overflow weirs of the pans down to the bottom of the column U, from whence it passes into the pipe E and cock R this cock throttling the to the pressure obtaining at the inlet F, where the liquefied oxygen is discharged.

The oxygen cooled by the throttling and discharged through F fills the top pans G, and the liquid contained in these pans becomes richer in oxygen according as it drops from the higher into the lower pans over the existing overflow weirs until it reaches and fills the vessels H and H and the outside of the heat exchange apparatus I.

In this manner oxygen free from nitrogen is obtained at the bottom, and nitrogen free from oxygen is obtained at the top.

The totally liquefied nitrogen in the pipes L, whose top ends are closed, by filling the pans M holds back the oxygen,- which then descends to the bottom over the overflow weirs. The top pan M will therefore contain practically pure nitrogen. This liquid nitrogen, after having been throttled by the cock R enters the rectifying column through the inlet V and fills the top pans thereof thus serving to rectify the nitrogen which, being displaced by the residual oxygen, disengages itself, the said oxygen in its turn being con-- densed. K is the nitrogen vapors outlet, the nitrogen vapors descending down to L, where they divide into a stream -mwhich circulates in the outer pipe of the heat exchange apparatus S and a stream y which circulates in the outer pipe of the heat-exchange apparatus S in order to cool down the air circulating through the said pipes.

The portion 3/ of nitrogen, after flowing g in refrigerating the air to approximately the initial expanding temperature.

Having now particularly described and ascertained the nature of my said invention and in what manner the same is to be performed, I declare that What I claim is A process for the production of oxygen and nitrogen from air with a rectifying column comprising compressing and cooling a portion of said air at very low pressure, subjecting the same successively to selective liquefaction under pressure in the lower part of said rectifying column, compressing and cooling the remaining air at a higher pressure than aforementioned, expanding a subdivision of said remaining air with-external work, introducing the same under pressure into the lower part of said rectifying column, selectively liquefying said subdivision under the aforesaid very low pressure, entirely liquefying a. second subdivision'of said remaining air without modifying the pressure thereof, throttlin said second subdivision of liquid air introt ucing the same into the lower part of said rectifying column separately collecting condensed liquid oxygen in the bottom and the liquid nitrogen intermediately of said liquefying column. 

